(a) Technical Field
The present invention relates to a method for preparing a carbon nanomaterial/polymer composite. More particularly, it relates to an improved method for preparing a carbon nanomaterial/polymer composite capable of solving a dust problem of a carbon nanomaterial powder and a layer separation problem due to large density difference between the carbon nanomaterial powder and a polymer pellet and providing superior physical properties of the composite, whereby an additive used to prepare the carbon nanomaterial/polymer composite is mixed with the carbon nanomaterial powder and prepared into a pellet, which is then mixed with the polymer pellet.
(b) Background Art
Carbon nanomaterials include fullerene, carbon nanotube (CNT), graphene, graphite nanoplate, etc. Among them, a carbon nanotube has a cylindrical nanostructure with a honeycomb-shaped sheet of graphite rolled to a diameter of nanometer scale and has specific characteristics depending on shape. The carbon nanotube is light since it has a hollow space, has good electrical conductivity comparable to that of copper, has good thermal conductivity comparable to that of diamond and has good tensile strength comparable to that of steel. It is also categorized as single-walled carbon nanotube (SWCNT), multi-walled carbon nanotube (MWCNT) or rope carbon nanotube according to the rolling type.
Owing to its superior physical properties, the carbon nanotube is drawing attentions as filler of various polymer composites, including antistatic polymer composites, EMI-shielding polymer composites, heat-resistant polymer composites, high-strength polymer composite, and so forth. In particular, many researches and developments are underway for commercialization of polymer composites using the carbon nanotube.
However, despite the R&D efforts, the dust problem due to low apparent density of carbon nanotube powder and health issue arising therefrom, layer separation occurring when the carbon nanotube is supplied together with a polymer pellet to an extruder to prepare a polymer composite due to the large density difference of the carbon nanomaterial powder and the polymer pellet, and dispersion problem of the carbon nanotube as a result thereof remain obstacles to large-scale use of the carbon nanotube. Although an additive is commonly added to improve dispersibility of the carbon nanotube in the melted polymer, further studies are necessary to achieve better dispersion effect with the same amount of the additive.
Methods for preparing a carbon nanomaterial/polymer composite by adding an additive disclosed in the published patents include the followings.
World Tube Co., Ltd.'s Korean Patent No. 10-0955295 titled “Manufacturing method of shaped solid comprising nanocarbon” discloses a shaped solid comprising a nanocarbon, a metal (including oxide and ion) and a resin. However, since the prepared shaped solid comprises the metal and the resin, when it is used in a polymer composite, a polymer used as a matrix may react with or be incompatible with the metal and the resin included in the solid, resulting in degradation of important physical properties of the nanocarbon.
Korean Patent Publication No. 2011-0065704 titled “Manufacturing method of nanocarbon shaped body and manufacturing method of nanocarbon shaped body, nanocarbon dispersed solution and nanocarbon material using same” discloses a method for manufacturing a nanocarbon shaped body comprising cutting a nanocarbon, mixing the nanocarbon with a dispersant and a solvent and dispersing the nanocarbon using a dispersing apparatus, flocculating the nanocarbon dispersed solution into a nanocarbon sludge by further adding a coagulant, removing a liquid component from the nanocarbon sludge and crushing or pulverizing same into a nanocarbon powder, and shaping the nanocarbon powder and drying same to prepare a nanocarbon shaped body. However, although a metal or a resin is not included in the nanocarbon shaped body, when it is used in a polymer composite, a polymer used as a matrix may react with or be incompatible with the dispersant and the coagulant remaining in the solid, resulting in degradation of important physical properties of the nanocarbon.
Further, developments of a specific additive for improving dispersibility of a carbon nanotube in a melted polymer or uses of a combination of the existing additives are disclosed with regard to the preparation of the carbon nanotube/polymer composite. However, few researches and developments have been made as to how to supply the carbon nanotube to improve dispersibility of the carbon nanotube in a melted polymer.